Here, the only formally unsaturated aromatics differ from the other unsaturated compounds: due to the high stability of the aromatic system, aromatics do not carry out the typical addition reactions or only under extreme conditions such as high temperature or high pressure. Instead, substitution reactions are preferred.

Unsaturated compounds are generally more reactive than saturated compounds. Triglycerides (rapeseed oil, linseed oil, olive oil, etc.) with a high content of unsaturated fatty acid residues turn more rapidly rancid than those with a high proportion of saturated fatty acid residues ,as for example coconut fat.

In a long chain of carbons, such as a fatty acid, a double or triple bond will cause a kink in the chain. These kinks have macro-structural implications. Unsaturated fats tend to be liquid at room temperature, rather than solid, as the kinks in the chain prevent the molecules from packing closely together to form a solid. These fats are called oils and are present in fish and plants.

In other unsaturated hydrocarbons, the double bond between two carbons prevents rotation of the atoms about the bond, locking them into specific structural formations. When attached atoms occupy similar positions on each carbon, they are referred to as "cis", and when they are on opposite sides, they are called "trans". Most natural hydrocarbons exist in the cis state, but artificially manufactured hydrocarbons are trans. The body lacks the enzymes to properly break down the trans configuration. This is why trans fats are viewed as dangerous and unhealthy, as they tend to build up. Unsaturated compounds of the two formations are classified as geometric isomers of one another.

The amount of unsaturation of a fatty acid can be determined by finding its iodine number.